1. Field of the Invention
The present invention relates to an electrochromic anti-glare mirror, used for automotive interior and exterior rearview mirrors, and especially to a seal structure for an all-solid electrochromic anti-glare mirror.
2. Description of the Related Art
It is known that an electrochromic optical device controls the occurrence and extinction of redox reaction which generates a color when the electrochromic material is charged with an electric field. Recently, the electrochromic optical device has been used for anti-glare mirrors.
FIG. 1 and FIG. 2 show the prior art of the structure of an electrochromic anti-glare mirror. FIG. 1 shows a flat type electrochromic anti-glare mirror. The flat type electrochromic anti-glare mirror 1 comprises a flat, transparent glass substrate 2, the back face of which is coated with a transparent conductive coating 3, an all-solid electrochromic layer 4, and a transparent reflective-conductive coating 5. Both of the electrochromic layer 4 and the reflective-conductive coating 5 are covered with a sealing resin 6. A sealing glass plate 7 is attached to the back surface of the sealing resin 6.
The all-solid electrochromic layer 4 comprises an iridium oxide film 8 as an oxide color-forming film, a Ta.sub.2 O.sub.5 film 9 as an electrolyte film, and a WO.sub.3 film 10 as a reductive color-forming film. The reflective-conductive coating 5 comprises an Al film. These films 8, 9, 10 are laminated by a process such as vapor deposition.
Color formation and extinction is described as follows. The iridium oxide film 8 contains H.sub.2 O in the form of Ir(OH).sub.n. When a terminal 3a of the transparent conductive coating 3 is connected to a positive terminal of a DC power source, and a terminal 5a of the reflective-conductive coating 5 is connected to a negative terminal of the DC power source, H.sup.+ protons move in the iridium oxide film 8 to the Ta.sub.2 O.sub.5 film 9, and e.sup.- electrons are released into the transparent conductive coating 3. As a result, oxidation occurs in the Ta.sub.2 O.sub.5 film 9 to generate a color, as follows: EQU Ir(OH).sub.n .fwdarw.IrO.sub.X (OH).sub.n-x (forming color)+xH.sup.+ +xe-
H.sup.+ protons migrate from the Ta.sub.2 O.sub.5 film 9 to the WO.sub.3 film 10, and e.sup.- electrons move from the reflective-conductive coating 5 into the WO.sub.3 film 10. As a result, reduction occurs in the WO.sub.3 film 10 to generate a color. EQU WO.sub.3 +xH.sup.+ +xe-.fwdarw.H.sub.x WO.sub.3 (forming color)
When reversing the DC power positive and negative terminals, reduction occurs in the iridium oxide film 8 to extinguish the color, and oxidation occurs in the WO.sub.3 film 10 to generate the color, wherein H.sub.2 O contained in the Ta.sub.2 O.sub.5 film 9 is ionized to convert to H.sup.+ protons and OH.sup.- ions which contribute highly to color formation and extinction.
The sealing glass plate 7 is used to support the electrochromic layer 4 and the reflective-conductive coating 5 by providing mechanical strength from the outside surface, and to increase its resistance to water, moisture, and corrosion. Furthermore, the sealing glass plate 7 blocks ion migration to prevent radiating H.sup.+ protons and OH.sup.- ions from the coating and absorbing the same from the outside so as to maintain the quantity of H.sup.+ protons and OH.sup.- ions contained in the electrochromic layer 4 at a constant level. As a result, the reaction of color formation and extinction is maintained preferably in the electrochromic layer 4.
FIG. 2 shows the conventional structure of an electrochromic anti-glare mirror of a curved type. This type of the electrochromic anti-glare mirror (the curved type mirror) 11 has very nearly the same structure as the above-mentioned flat type. The curved type mirror 11 comprises a flat, transparent glass substrate 12, a transparent conductive coating 13, an all-solid electrochromic layer 14, a reflective-conductive coating 15, and a sealing plate 17. However, each of the above-mentioned elements is formed in a desired curved shape. As a result, the whole structure of the mirror 11 has a curvature.
The all-solid electrochromic layer 14 comprises an iridium oxide film 18 as an oxide color-forming film, a Ta.sub.2 O.sub.5 film 19 as an electrolyte film, and a WO.sub.3 film 20 as a reductive color-forming film. The conductive coating 15 comprises an Al film. These films 18, 19, 20 are laminated by a process such as vapor deposition.
In the above electrochromic anti-glare mirror 1/11, when a voltage is applied between the transparent conductive coating 3/13 and the reflective-conductive coating 5/15, both of the iridium oxide film 8/18 and the WO.sub.3 film 10/20 promote redox reaction as described above to generate a color, thereby reducing reflection of the mirror.
Reducing the reflection rate of the mirror makes it possible to reduce glare of reflecting light caused by headlights of a vehicle to the rear. When a voltage is applied in the opposite direction, each of the iridium oxide film 8/18 and the W.sub.3 film 10/20 promotes redox reaction in the reverse direction. As a result, the color is extinguished, thereby causing a reflection rate in a usual range.
There are several problems to be solved for the conventional electrochromic anti-glare mirrors:
(1) The weight of the electrochromic anti-glare mirror 1/11 is heavy because of the sealing glass plate 7/17. The sealing glass plate 7/17 serves to block ion migration to maintain the function of the all-solid electrochromic film 4/14 at a normal level. Thus, the problems cannot be solved simply by removing the sealing glass plate 7/17.
(2) In the curved type mirror 11, the curvature of the sealing glass plate 17 must coincide with the curvature of the glass substrate 12. If there is a difference in curvature between the sealing glass plate 17 and the glass substrate 12, an uneven gap and an uneven thickness of the sealing resin disposed between the sealing glass plate 17 and the glass substrate 12 occur. The unevenness causes internal stress in the mirror 11, easily separating the elements of the mirror.
(3) In production of the curved type mirror 11, it is costly to achieve high accuracy of the curvature of both the sealing glass plate 17 and the glass substrate 12.